1. Field of the Invention
This invention relates to a coating material gunned onto the inner surface of the base refractories of continuous caster tundishes, and more particularly to a lightweight heat insulating coating material for dry gunning featuring lightness in weight, good heat insulating properties, and excellent abilities to prevent thermal erosion by slag, permeation of slag and liquid steel, and sticking to the base refractories.
2. Description of the Prior Art
For coating the inner surface of the base refractories of continuous caster tundishes, basic refractories have been used, with consideration given to the needs to prevent thermal erosion by slag, facilitate skull removal and assure production of clean steels.
As the amount of continuous casting increases in steelmaking, increasingly severe requirements have come to be set for the upgrading of steel quality and prolonging the life of tundish refractories. Requirements for the coating material (the refractories gunned onto the inner surface of the base refractories of tundishes are hereinafter called the "coating material") also have grown more exacting.
To satisfy such trade demands, efforts are continuing to achieve greater weight reduction and provide better heat insulating properties. Weight reduction and enhancement of heat insulating properties will make it possible to prolong the life of the coating material and base refractories by preventing the coating material from sticking to the base refractories and decreasing the thermal load imposed on the inner base refractories of tundishes. The same measures also result in saving energy consumption, which, in turn, permits cutting down the overall costs of tundishes.
The two main conventional measured adopted for the weight reduction of the coating material are as follows: A first method was to decrease the bulk density of the material by producing a foam matrix while the material is being kneaded with water. This type of material is used mainly in troweling and wet gunning. Another method achieves bulk density reduction by dispersing organic or inorganic fibers in the matrix. This latter type of material is applied mainly by dry gunning. The aforementioned two methods reduce the bulk density of the whole coating material by creating crevices in the matrix by means of foaming and fibers. The original matrix has already been made weaker than the base refractories by the use of the binder and other additives. Then, such measures make the matrix still weaker, thereby making the matrix more susceptible to slag erosion and the permeation of slag and liquid steel. To offset such disadvantages, such remedial measures as reduction in foam size by means of a foam sizing agent and the use of shorter fibers have come to be adopted. Notwithstanding such corrective measures, however, it has remained substantially unchanged that the aforementioned two types of methods depend on the crevices formed in the matrix for the reduction of bulk density and the enhancement of heat insulating properties. And such crevices, though reduced in size, make it impossible to completely prevent the permeation of slag and liquid steel. As such, there is a strong demand for further preventing thermal slag erosion and the permeation of both slag and liquid steel.